DLPX-88488 profile is missing stack traces#16
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…tacktrace (#4902)
offcputime may display inaccurate DSO information in the stacktrace.
Here's an example of the issue:
It shows the same DSO offset for different addresses, which is incorrect.
$ ./offcputime -v
..
#14 0x00007f8b912a8c (/usr/lib/libcbe.so_0x22afa8c)
#15 0x000044000a3ee0 (/usr/lib/libcbe.so_0x22afa8c)
#16 0x000044001fc56c (/usr/lib/libcbe.so_0x22afa8c)
This is why syms__map_addr_dso simply returns NULL when syms__find_dso also
returns NULL. In that case, the values of dso_name and dso_offset are not
changed. If the dso_name and dso_offset variables have a garbage value before
calling syms__map_addr_dso, those garbage values are maintained after calling
syms__map_addr_dso.
This patch fixes the issue by reinitializing dso_name and dso_offset variables
before calling syms__map_addr_dso.
Co-authored-by: Eunseon Lee <es.lee@lge.com>
tonynguien
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offcputime may display inaccurate DSO information in the stacktrace.
Here's an example of the issue:
It shows the same DSO offset for different addresses, which is incorrect.
$ ./offcputime -v
..
#14 0x00007f8b912a8c (/usr/lib/libcbe.so_0x22afa8c)
#15 0x000044000a3ee0 (/usr/lib/libcbe.so_0x22afa8c)
#16 0x000044001fc56c (/usr/lib/libcbe.so_0x22afa8c)
This is why syms__map_addr_dso simply returns NULL when syms__find_dso also
returns NULL. In that case, the values of dso_name and dso_offset are not
changed. If the dso_name and dso_offset variables have a garbage value before
calling syms__map_addr_dso, those garbage values are maintained after calling
syms__map_addr_dso.
To ensure consistent usage of DSO info and symbol info, the prototype of
syms__map_addr_dso has been modified to be similar to dladdr[1].
This is the prototype of dladdr:
int dladdr(void *addr, Dl_info *info);
The information is returned in a Dl_info structure. If no symbol matching addr
could be found, then dli_sname and dli_saddr are set to NULL.
typedef struct {
const char *dli_fname; /* Pathname of shared object that
contains address */
void *dli_fbase; /* Base address at which shared
object is loaded */
const char *dli_sname; /* Name of symbol whose definition
overlaps addr */
void *dli_saddr; /* Exact address of symbol named
in dli_sname */
} Dl_info;
Similarly, if no symbol matching the addr could be found, then sym_name and
sym_offset are set to NULL in syms__map_addr_dso of this patch.
Also, apply the modified API usage to offcputime, futexctn, and memleak.
[1] https://man7.org/linux/man-pages/man3/dladdr.3.html
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Clean cherrypick of b2e9c36
Testing: ab-pre-push passed
Ran the following to figure out number of entries on a 4 core system
without the change:
"""
delphix@ip-10-110-214-21:/var/delphix/server/log/stats$ grep -v '^-' profile_3600.log | grep -o ' [0-9]$' | paste -s -d+ - | bc
721214
"""
721214/(6060499) = ~50% hit rate
with the change:
"""
delphix@ip-10-110-238-208:/var/delphix/server/log/stats$ grep -v '2023-11-01' profile_3600.log | grep -o ' [0-9]$' | paste -s -d+ - | bc
1237787
"""
1237787/(6060499) = ~80% hit rate
I doubled the default hash to 81920 and we got to 83% hit rate, does not seem like we gain too much with increasing the hash size.